KR101328826B1 - Liquid crystal display and method of local dimming thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device, comprising: a display panel; A backlight unit including light sources; The light emitting surface of the display panel and the backlight unit is divided into a plurality of blocks, and an input image is divided into the blocks to determine the specific value according to a luminance difference between a specific block and neighboring blocks and a degree of gradation of the specific block. A representative value adjusting unit for outputting a modified block representative value by adjusting the original block representative value of the block; A dimming value determiner configured to select a dimming value for each block of the specific block by mapping the corrected block representative value to a substantially linear dimming curve; And a light source driving unit configured to drive light sources for irradiating light to a specific block of the backlight unit according to the dimming value of each block to irradiate light to a specific block of the display panel.

Description

Liquid crystal display and local dimming method {LIQUID CRYSTAL DISPLAY AND METHOD OF LOCAL DIMMING THEREOF}

The present invention relates to a liquid crystal display and a local dimming method thereof.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. The transmissive liquid crystal display displays an image by controlling an electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

The image quality of the liquid crystal display device depends on the contrast characteristics. Only the method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer of the liquid crystal display panel has a limitation in improving the contrast characteristic. In order to improve the contrast characteristic, a backlight dimming control method for adjusting the brightness of the backlight according to an image has been developed, which has dramatically improved the contrast characteristic. The backlight dimming control method may reduce power consumption by adaptively adjusting the brightness of the backlight according to the input image. The backlight dimming method includes a global dimming method for adjusting the luminance of the entire display surface and a local dimming method for dividing the display screen into a plurality of blocks and locally adjusting the luminance of the display surface. have.

The global dimming method may improve dynamic contrast measured between the previous frame and the next frame. The local dimming method locally improves the brightness of the display surface within one frame period, thereby improving static contrast, which is difficult to improve with the global dimming method.

The local dimming method divides the backlight into a plurality of blocks to increase the backlight luminance of a block in which the image is bright, while lowering the backlight luminance of a block in which the image is relatively dark. The backlight brightness of the local dimming method is smaller than the backlight brightness of the entire light sources because the light sources are turned on for each block. In order to compensate for the low backlight luminance of the local dimming method, the pixel data may be compensated by multiplying the pixel data by a predetermined gain. When the pixel data is compensated for in the local dimming method, image quality deterioration, such as gray level aggregation, in which high grays have the same brightness may occur. In order to reduce such deterioration of image quality, a dimming curve in which a dimming curve for selecting a dimming value (%) according to a representative value of each block may be increased in most gray levels. In this case, the image quality is improved, but since the dimming value (%) is increased in most typical block-by-block representative values, the power consumption reduction effect is low.

The present invention provides a liquid crystal display and a local dimming method for maximizing the power consumption reduction effect and increasing the image quality at the time of local dimming.

The liquid crystal display of the present invention includes a display panel; A backlight unit including light sources; The light emitting surface of the display panel and the backlight unit is divided into a plurality of blocks, and an input image is divided into the blocks to determine the specific value according to a luminance difference between a specific block and neighboring blocks and a degree of gradation of the specific block. A representative value adjusting unit for outputting a modified block representative value by adjusting the original block representative value of the block; A dimming value determiner configured to select a dimming value for each block of the specific block by mapping the corrected block representative value to a substantially linear dimming curve; And a light source driving unit configured to drive light sources for irradiating light to a specific block of the backlight unit according to the dimming value of each block to irradiate light to a specific block of the display panel.

The liquid crystal display may further include: a first representative value calculator configured to calculate a representative value of each of the block images divided into the blocks in the input image; And a second representative value calculator configured to calculate an overall representative value for one frame image of the input image.

The representative value adjusting unit may include: a first representative value adjusting unit configured to upwardly adjust the block representative value by a predicted value determined according to a difference between the block representative value and the total representative value of the specific block; A second representative value adjusting unit which determines a weight according to the gradation degree; And an adder for adding the weighted value to the original block representative to output the corrected block representative.

The liquid crystal display may further include: a pixel-specific light amount calculator configured to calculate a light amount of each pixel in the specific block by selecting a light profile preset as the dimming value for each block; A gain adjusting unit calculating gain for each pixel in the specific block based on the amount of light of each of the pixels, and multiplying the gain by the pixel data to output pixel data compensation values of the specific block; And an image quality evaluation unit for calculating a degree of gray level aggregation of the specific block based on the pixel data compensation values of the specific block and inputting the result to the second representative value adjusting unit.

The local dimming method of the liquid crystal display may include dividing a light emitting surface of the display panel and the backlight unit into a plurality of blocks; Dividing the input image into the blocks; Generating a corrected block representative value by adjusting a raw block representative value of the specific block according to a luminance difference between a specific block and neighboring blocks and a degree of gradation of the specific block; Determining the block-specific dimming value of the specific block by mapping the corrected block representative value to a substantially linear dimming curve; And illuminating a specific block of the display panel by driving light sources for irradiating light to a specific block of the backlight unit according to the dimming value of each block.

The present invention maximizes the power consumption reduction effect by using a low dimming curve, as well as by adaptively adjusting the block representative value by predicting the luminance difference between specific blocks and neighboring blocks and the degree of gradation of specific blocks. The image quality at the time of dimming can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, when it is determined that a detailed description of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The component name used in the following description may be selected in consideration of easiness of specification, and may be different from the actual product name.

Before describing an embodiment of the present invention, changes in image quality and power consumption according to whether or not compensation of pixel data and selection of a dimming curve in the local dimming method will be described with reference to FIGS. 1 to 4C.

The local dimming method divides the display screen into a plurality of blocks, derives a representative value for each block of the input image, and then maps the representative value for each block to a dimming curve to select a dimming value (%) for each block. do. The representative value for each block may be calculated as an average value or average picture level (APL) of the input image. The average value of the input image is the average value of the highest values among the RGB values of the pixel, and the average image level APL is the average value of the luminance values Y of the pixels. The dimming curve may be previously set in a look-up table as a characteristic expression that defines a dimming value (%) to be applied to local dimming of the corresponding block according to the representative value of each block of the input image.

The dimming curve may be selected as a high dimming curve as shown in FIG. 1 or a low dimming curve as shown in FIG. 1 and 2, the horizontal axis represents a representative value for each block, and the vertical axis represents a dimming value (%). In the high dimming curve as shown in FIG. 1, as the gray level increases, the dimming value (%) increases exponentially. 2, the dimming value (%) increases linearly in proportion to the gray level. FIG. 1 has a higher dimming value (%) at almost all gray levels than FIG. 2. If the dimming value (%) is high, the driving power of the backlight light source is high, so the power consumption is high. Although FIG. 2 is advantageous in terms of power consumption compared to FIG. 1, the image quality may be lowered as can be seen from the experimental results of FIGS. 3A to 4C.

3A to 3C are experimental result images of local dimming with a high dimming curve and a low dimming curve without compensating pixel data in the local dimming method.

When the representative value of each block of the original image as shown in FIG. 3A is mapped to the high dimming curve as shown in FIG. 1, the dimming value (%) is selected for each block to control the backlight luminance for each block, and the pixel data is not compensated. As shown in FIG. 3B, the overall luminance of the display image is lowered. On the other hand, by mapping a representative value for each block of the original image as shown in FIG. 3A to a low dimming curve as shown in FIG. 2, the dimming value (%) is selected for each block to control the backlight luminance for each block, As shown in 3c, the overall luminance of the display image is lowered and no detail is expressed. Therefore, in the case of not compensating pixel data at the time of local dimming, the high dimming curve as shown in FIG. 1 is excellent in image quality, but as described above, the high dimming curve consumes more power than the low dimming curve.

4A to 4C are experimental result images of performing local dimming with a high dimming curve and a low dimming curve in parallel with compensation of pixel data in the local dimming method.

By mapping a representative value of each block of the original image as shown in FIG. 4A to a high dimming curve as shown in FIG. 1, selecting a dimming value (%) for each block to control backlight luminance for each block and simultaneously performing pixel data compensation. Over-compensation of the pixel data in the bright part of the image results in a gradation aggregation phenomenon in which the bright gradations are displayed at the same luminance. Mapping a representative value of each block of the original image as shown in FIG. 4A to a low dimming curve as shown in FIG. 2, selecting a dimming value (%) for each block to control backlight luminance for each block, and simultaneously performing pixel data compensation as shown in FIG. 4C. Over-compensation of pixel data causes gradation aggregation to become more severe. Therefore, the high dimming curve as shown in FIG. 1 is excellent in image quality when the pixel data is compensated at the time of local dimming. However, as described above, the high dimming curve consumes more power than the low dimming curve.

According to the present invention, local dimming is performed based on a dimming curve as shown in FIG.

5 to 7 show a liquid crystal display according to an embodiment of the present invention.

5 to 7, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a source driver 12 for driving data lines 14 of the liquid crystal display panel 10, The gate driver 13 for driving the gate lines 15 of the liquid crystal display panel 10, the timing controller 11 for controlling the source driver 12 and the gate driver 13, and the liquid crystal display panel 10. And a backlight unit 20 for irradiating the light, a light source driver 21 for driving the light sources of the backlight unit 20, and a local dimming controller 16 for controlling local dimming.

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. A plurality of data lines 14 and a plurality of gate lines 15 are intersected with each other on a lower glass substrate of the liquid crystal display panel 10. Due to the cross structure of the data lines 14 and the gate lines 15, the liquid crystal cells Clc are arranged in a matrix form as shown in FIG. 6. The lower glass substrate of the liquid crystal display panel 10 includes data lines 14, gate lines 15, a thin film transistor TFT, a pixel electrode of a liquid crystal cell Clc connected to the thin film transistor TFT, and storage. A capacitor Cst or the like is formed.

A black matrix, a color filter, and a common electrode are formed on the upper glass substrate of the liquid crystal display panel 10. The common electrode is formed on the upper glass substrate in a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode, and a horizontal electric field such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode in the driving method. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The pixel array of the liquid crystal display panel 10 and the light emitting surface of the backlight unit 20 opposite thereto are divided into a plurality of blocks B11 to B45 as shown in FIG. 7 for local dimming. Each of the blocks B11 to B45 includes i × j (i and j are positive integers of 2 or more) pixels, and a backlight emitting surface irradiating light to the pixels. Each pixel includes subpixels of three primary colors or more, and the subpixel includes one liquid crystal cell Clc.

The timing controller 11 receives timing signals Vsync, Hsync, DE, and DCLK from an external system board, and supplies digital video data RGB to the source driver 12. The timing signals Vsync, Hsync, DE and DCLK include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a dot clock signal DCLK. The timing controller 11 controls timings of the operation of the source driver 12 and the gate driver 13 based on timing signals Vsync, Hsync, DE, and DCLK from an external system board. , GDC). The system board or the timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz, multiplies the source timing control signal DDC and the gate timing control signal GDC to 60 × N. (N is a positive integer of 2 or more) The operation of the source driver 12 and the gate driver 13 can be controlled at a frame frequency of Hz.

The timing controller 11 supplies digital video data RGB of an input image input from an external system board to the local dimming controller 16, and modulates the digital video data R ′ modulated by the local dimming controller 16. G'B 'is supplied to the source driver 12.

The source driver 12 latches the digital video data R'G'B 'under the control of the timing controller 11. The source driver 12 converts the digital video data R'G'B 'into positive / negative analog data voltages using the positive / negative gamma compensation voltages and supplies them to the data lines 14. .

The gate driver 13 includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving a TFT of a liquid crystal cell, an output buffer, and the like. The gate driver 13 is configured of a plurality of gate drive integrated circuits and sequentially outputs gate pulses (or scan pulses) having a pulse width of approximately one horizontal period. The gate pulse is sequentially supplied to the gate lines 15 in synchronization with the data voltages supplied to the data lines 14.

The backlight unit 20 is disposed under the liquid crystal display panel 10. The backlight unit 20 uniformly irradiates light to the liquid crystal display panel 10 including a plurality of light sources individually controlled for each block by the light source driver 21. The backlight unit 20 may be implemented as a direct type backlight unit or an edge type backlight unit. The light source of the backlight unit may include at least one of a hot cathode fluorescent lamp (HCFL), a cold cathode fluorescent lamp (CCFL), an external electro fluorescent lamp (EEFL), and a light emitting diode (LED).

The light source driver 21 individually controls the light sources of the backlight unit 20 block by pulse width modulation (PWM) in which the duty ratio is changed according to the dimming value BLdim input from the local dimming controller 16. . The pulse width modulated signal PWM controls the ratio of turning on and off the light sources, and the duty ratio% is determined according to the dimming value BLdim output from the local dimming control unit 16.

The local dimming controller 16 analyzes the digital video data RGB input from the timing controller 11 for each block as shown in FIG. 7 and calculates a representative value for each block of the blocks. The local dimming control unit 16 maps the representative value for each block to the low dimming curve as shown in FIG. 2, outputs the dimming value BLdim for each block of the backlight unit 20, and receives digital video data input from the timing controller 11. The RGB is modulated to compensate for pixel data to be displayed on the liquid crystal display panel 10. The local dimming control unit 16 predicts, according to a predetermined rule, a block image whose image quality may deteriorate when the low dimming curve of FIG. 2 is simply applied, and increases a representative value of each block of the corresponding block when such a block image is input. Adjust the block dimming value (BLdim).

FIG. 8 is a block diagram illustrating in detail the local dimming controller 16 shown in FIG. 5.

Referring to FIG. 8, the local dimming controller 16 may determine a first representative value calculator 81, a second representative value calculator 82, a first representative value adjuster 83, an adder 84, and determine a dimming value. A unit 85, a pixel-specific light amount calculation unit 86, a gain correction unit 87, an image quality evaluation unit 88, and a second representative value adjustment unit 83 are provided.

The first representative value calculator 81 calculates a block representative value of the input image. The second representative value calculator 82 calculates the total representative values for the input image of one frame. The block representative value and the total representative value are calculated as an average value or an average image level (APL).

If the block-specific representative value of a specific block is higher than the total representative value, the brightness of neighboring blocks is low when local dimming is performed based on the original block representative value. There is a possibility. In consideration of this, the first representative value adjusting unit 83 selectively adjusts the original block representative value through the following process. The first representative value adjusting unit 83 calculates a difference between the block representative value of the specific block and the entire representative value. The first representative value adjusting unit 83 increases the block representative value as shown in FIG. 11 by a preset prediction value according to the difference between the block representative value and the total representative value. The predicted value is determined by preliminary experiments with the higher the difference between the block representative value and the total representative value.

The adder 84 adds the weight from the second representative value adjusting unit 89 to the block representative value of the specific block input from the first representative value adjusting unit 83 and outputs a modified block representative value. .

The dimming value determiner 85 maps the corrected block representative value to a low dimming curve as shown in FIG. 11, selects the dimming value BLdim for each block, and outputs the dimming value BLdim to the light source driver 21 and the pixel amount calculating unit 86. . The dimming value determiner 85 may select a dimming value BLdim for each block by using the lookup table. The lookup table receives a correction block representative value and selects and outputs a block-specific dimming value BLdim from a pre-stored dimming curve using the correction block representative value as an address. The light source driver 21 controls the luminance of the light sources of the backlight unit 20 block-by-block with pulse width modulation PWM in response to the dimming value BLdim for each block.

The pixel-specific light amount calculator 86 selects a light profile preset as a dimming value for each block and calculates the amount of light for each pixel in a specific block. The light profile may be calculated as the sum of the amount of light of a specific pixel and the amount of light reaching the specific pixel from the surrounding pixels of the specific pixel at the time of local dimming, and local dimming by block dimming value BLdim for each pixel It can be determined through a preliminary experiment to measure the luminance.

The gain correction unit 87 calculates a gain for each pixel and multiplies the gain by the original pixel data to compensate for the pixel data. The gain is calculated as the ratio of the pixel light amount when the light sources of the backlight unit 20 are turned on at full white (full white or full brightness) (non-local dimming) and the pixel light amount calculated through the light profile at local dimming. do. That is, the gain G is calculated as G = K _normal / K _local . Here, K _normal is a constant value indicating the amount of light when full white without local dimming, that is, when the entire backlight emitting surface is lit in full white. K _local is a variable value indicating the amount of light of a specific block according to the dimming value BLdim for each block when performing local dimming.

The image quality evaluator 88 analyzes pixel data compensation values of a specific block input from the gain compensator 87, calculates a degree of gray level aggregation, and outputs a gray level prediction value. The image quality evaluator 88 calculates the number of white gray scale data among the pixel data compensation values of a specific block. The gray level of the pixel data may be determined as a most significant bit (MSB). For example, when the MSB is "11", the data may be determined as white gray data, when the MSB is '00', as black gray pixel data, and when the MSB is '01', the gray gray data. If the number of white gray scale data is greater than a predetermined reference value, the image quality evaluator 88 determines that gray scales appear in a specific block. The gray scale prediction value calculated by the image quality evaluation unit 88 has a higher value as the number of white gray scale data increases.

The second representative value adjusting unit 89 selects a weight based on the gray level predictive value input from the image quality evaluating unit 88 and feeds it back to the adder 84. The second representative value adjusting unit 89 may be implemented as a lookup table that selects weights according to the gradation prediction value, or as an arithmetic logic circuit that calculates the weight according to the gradation prediction value. The weight may vary in proportion to the gray scale prediction value.

Hereinafter, a local dimming example of the present invention will be described with reference to FIGS. 9 to 11. FIG. 9 is a diagram illustrating a first image in which pixels of a full screen are composed of halftone pixel data. FIG. 10 is a second image in which the background is darker than the first image, and " Ray " Assume that the image in the center box in each of the images is the specific block described above.

The average image level APL of the specific block of FIG. 9 and the specific block of FIG. 10 is equal to '127'. In the conventional local dimming method, since a specific block of FIG. 9 and a specific block of FIG. 10 have the same block representative value, that is, the average image level APL is the same, dimming is mapped to the same dimming value (representative value "gray" in FIG. 11). Value) to local dimming of a particular block. In this case, in the specific block of FIG. 10, gray saturation occurs due to the sum of the low dimming value and the pixel data compensation, resulting in gray level aggregation in which similar white gray levels are seen as the same gray scale. In contrast, the local dimming method of the present invention analyzes a specific block image of FIG. 10 to predict a luminance difference between a specific pixel and its surrounding pixels, and to predict the degree of gradation of gray levels within a specific pixel. The dimming value mapped to the representative value "gray" in 11 is adjusted upward (the dimming value mapped to the representative value "gray" in FIG. 11) to prevent deterioration of the image quality of a specific block. Here, the block representative value is adjusted upward by the image quality evaluator 88 until the number of white gray scale data becomes less than or equal to a predetermined reference value, that is, until the gray scale is eliminated.

FIG. 12 illustrates the effect of reducing power consumption when controlling local dimming with the high dimming curve # 1 of FIG. 1, and consumption when controlling local dimming with the low dimming curve # 2 of FIG. 11. A diagram showing the results of experiments comparing power reduction effects.

In this experiment, the non-local dimming power consumption when displaying the experimental image on the liquid crystal display by lighting the entire light sources of the backlight unit 20 in full white without performing local dimming was measured. In addition, the conventional local dimming when local dimming is performed using the high dimming curve # 1 of FIG. 1 to display the same experimental image on the same LCD while individually controlling the luminance of the light sources of the backlight unit 20 for each block. The power consumption and the local dimming power consumption of the present invention measured by the same method using the low gamma curve of FIG. 11 were measured. As a result of comparing the measurements, the conventional local dimming power consumption was reduced by 22% compared to the non-local dimming power consumption, and the dimming power consumption of the present invention was reduced by 51% compared to the non-local dimming power consumption. Accordingly, the present invention can significantly reduce the power consumption by using the low dimming curve of FIG. 11, and as described above, the block representative value is adapted by predicting the luminance difference between the specific block and the neighboring blocks and the degree of gradation of the specific block. As a result, the image quality during local dimming can be improved by adjusting upward.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

1 is a diagram illustrating an example of a high dimming curve.

2 is a diagram illustrating an example of a low dimming curve.

3A to 3C are experimental result images of local dimming with a high dimming curve and a low dimming curve without compensating pixel data in the local dimming method.

4A to 4C are experimental result images of performing local dimming with a high dimming curve and a low dimming curve in parallel with compensation of pixel data in the local dimming method.

5 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

6 is an equivalent circuit diagram of a part of a pixel array of the liquid crystal display panel illustrated in FIG. 5.

7 is a diagram illustrating blocks of local dimming.

FIG. 8 is a block diagram illustrating in detail the local dimming controller shown in FIG. 5.

9 and 10 are experimental images comparing the conventional local dimming method and the local dimming method of the present invention.

11 is a diagram illustrating an example of adjusting a representative value for each block.

FIG. 12 is a diagram illustrating an experimental result comparing the power consumption reduction effect of controlling local dimming with the high gamma curve of FIG. 1 and the power consumption reduction effect of controlling local dimming with the gamma curve of FIG. 11.

Description of the Related Art

10 liquid crystal display panel 16 local dimming control unit

20: backlight unit 81: first representative value calculation unit

82: second representative value calculation section 83: first representative value adjustment section

84: adder 85: dimming value determining unit

86: light amount calculation unit per pixel 87: gain correction unit

88: image quality evaluation unit 89: second representative value adjustment unit

Claims (8)

Display panel; A backlight unit including light sources; The light emitting surface of the display panel and the backlight unit is divided into a plurality of blocks, and an input image is divided into blocks, and a difference between a block representative value of a specific block and an entire representative value of one frame image of the input image is determined. A representative value adjusting unit for outputting a modified block representative value by adjusting the original block representative value of the specific block according to the degree of gradation of the specific block; A dimming value determiner configured to select a dimming value for each block of the specific block by mapping the corrected block representative value to a substantially linear dimming curve; And A light source driving unit configured to drive light sources for irradiating light to a specific block of the backlight unit according to the dimming value of each block, to irradiate light to a specific block of the display panel; And the degree of gray level aggregation is determined based on whether the number of white gray level data of each of the blocks is greater than a predetermined reference value. The method of claim 1, A first representative value calculator configured to calculate a representative value of each of the block images divided into the blocks in the input image; And And a second representative value calculator which calculates the total representative value. The method of claim 2, The representative value adjusting unit, A first representative value adjusting unit configured to adjust the block representative value upward by a predicted value determined according to a difference between the block representative value and the total representative value of the specific block; A second representative value adjusting unit which determines a weight according to the gradation degree; And An adder configured to add the weight to the original block representative value to output the corrected block representative value, And the predicted value is determined to be higher as the difference between the block representative value of the specific block and the total representative value increases. The method of claim 3, wherein A pixel-specific light amount calculator configured to calculate a light amount of each pixel in the specific block by selecting a light profile preset as the dimming value for each block; The gain is calculated for each pixel in the specific block according to the ratio of the pixel light amount when all the light sources of the backlight unit are turned to full white and the pixel light amount calculated through the light profile when local dimming, and the gain is added to the pixel data. A gain adjusting unit which multiplies and outputs pixel data compensation values of the specific block; And The higher the number of white gradation data among the pixel data compensation values of the specific block is, the higher the gradation of the gradation is. A liquid crystal display device, characterized in that provided. Dividing the light emitting surface of the display panel and the backlight unit into a plurality of blocks; Dividing an input image into the blocks; A corrected block representative value is generated by adjusting the original block representative value of the specific block according to the difference between the block representative value of the specific block and the overall representative value of the one-frame image of the input image and the degree of gradation of the specific block. step; Determining the block-specific dimming value of the specific block by mapping the corrected block representative value to a substantially linear dimming curve; And Irradiating light to a specific block of the display panel by driving light sources for irradiating light to a specific block of the backlight unit according to the dimming value of each block; And the degree of gray level aggregation is determined based on whether the number of white gray level data of each of the blocks is greater than a predetermined reference value. 6. The method of claim 5, Calculating a representative value of each of the block images divided into the blocks in the input image; And Comprising the step of calculating the total representative value of the local dimming method of the liquid crystal display device characterized in that it further comprises. The method of claim 6, Generating the correction block representative value, Adjusting the block representative value upward by a prediction value determined according to the difference between the block representative value and the total representative value of the specific block; Determining a weight according to the degree of gradation; And Adding the weight to the original block representative to generate the modified block representative; And the predicted value is determined to be higher as the difference between the block representative value of the specific block and the total representative value increases. The method of claim 7, wherein Calculating a light amount of each pixel in the specific block by selecting a light profile preset as the dimming value for each block; The gain is calculated for each pixel in the specific block according to the ratio of the pixel light amount when the light sources of the backlight unit are turned to full white and the pixel light amount calculated through the light profile when local dimming, and the gain is added to the pixel data. Multiplying to generate pixel data compensation values of the particular block; And Determining that the degree of gradation is higher as the number of white gradation data is greater than a predetermined reference value among the pixel data compensation values of the specific block, and outputting a result of determining the degree of gradation Local dimming method of the device.

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